A piezoresistive pressure transducer includes a number of piezoresistors placed near the edge of a diaphragm where the stress change is high under external pressure. Accordingly, external pressure on the diaphragm stresses the diaphragm, which affects the resistance of the piezoresistors. The change in resistance can be detected by external circuitry, and the change in resistance is used to determine the pressure applied to the diaphragm.
The miniaturization of sensors and electronic circuits is an ongoing effort for a multitude of applications in, for example, the consumer, industrial, medical, and automotive markets. Some miniaturized designs attempt to combine an application specific integrated circuit (ASIC) and a microelectromechanical systems (MEMS) sensor onto a single chip using, for example, a complementary metal oxide semiconductor (CMOS) fabrication process. A CMOS fabrication process can provide many logic gates and other digital circuits per unit area, is relatively inexpensive, and typically yields reliable circuits.
Unfortunately, process differences between a CMOS fabrication process and a piezoresistive pressure transducer fabrication process have complicated the development of a cost effective method for integrating a CMOS integrated circuit and a piezoresistive pressure transducer on a single chip. Thus, many piezoresistive pressure devices consist of a separate CMOS signal processing die and a pressure sensor die co-packaged through wirebonding to form the pressure sensor system. Such a configuration has the disadvantages of more complicated packaging, relatively large footprint, and relatively high cost. Some prior art methods of integrating a CMOS signal processor and a pressure sensor on a single chip use an electrochemical etch (ECE) method to form a pressure sensor cavity. Such integration methods using ECE methodology have the disadvantages of relatively complicated processing and high cost.